Fiber optic cables have become a highly desirable mode of transmission for telecommunication and other signals. However, the installation of fiber optic cables presents unique problems when compared to the installation of electrical conductor cables. The metallic electrical conductors of electrical conductor cables serve the dual functions of providing electrical conductivity and providing mechanical strength. On the other hand, while the materials included in fiber optic cables provide optical conductivity, they typically provide relatively little mechanical strength when compared to a typical electrical cable. Consequently, great care must be taken when installing fiber optic cables and exposing fiber optic cables to potential disturbance to prevent fiber optic cables from breaking or otherwise becoming damaged.
Submarine, or underwater, applications present particularly troublesome problems in the successful use of fiber optic cables. In an underwater application, a cable must be sufficiently dense so that it stays at the bottom of a body of water in which it is installed. Such a cable may constantly be acted upon by forces from currents in the body of water. In addition, an underwater cable may experience major disturbances caused by setting or raising boat anchors or other everyday, human-originated activities. Thus, underwater applications typically require the use of a stronger cable than is used in a conventional subterranean, or underground, application. One conventional submarine fiber optic cable includes a fiber filled cable with double armored steel strands and jute wrapping. Such a cable has a greater density and tensile strength than a typical subterranean fiber optic cable.
While the conventional submarine fiber optic cables have been successfully used in submarine applications, they provide undesirable solutions to underwater problems. The additional processing steps required to produce a conventional submarine fiber optic cable cause it to be excessively expensive. For example, a conventional double armored submarine fiber optic cable costs approximately seven times more than an otherwise generally equivalent conventional subterranean fiber optic cable.
In addition, the metallic materials included in the conventional submarine fiber optic cable are subject to electrolysis when installed in an underwater environment. The electrolysis produces OH ions from the metallic materials. The optically transmissive components of the fiber optic cable absorb these OH ions. Over time, an undesirably high signal attenuation characteristic results. For example, a conventional submarine fiber optic cable is specified as having a 3 dB/km attenuation factor while an otherwise generally equivalent subterranean fiber optic cable is specified as having a 0.5 dB/km attenuation factor.
Moreover, the conventional submarine fiber optic cable experiences manufacturing constraints which limit the unspliced section lengths to an undesirably short maximum length, which in one example is around 9800 feet. Thus, an excessive number of splices are required to install the conventional submarine fiber optic cable over extended underwater distances. Splices are undesirable because they increase attenuation, and they require a large amount of time during installation of the cable.
Furthermore, the splicing procedure for a conventional submarine fiber optic cable is an extremely time consuming and painstaking operation when compared to a typical subterranean fiber optic cable splice. Any fiber optic cable splice is a delicate operation to insure that signal attenuation is minimized. However, an additional factor complicates the splicing of the conventional submarine fiber optic cable. Specifically, the tensile strength of the cable must be preserved across the splice. In other words, the steel strands must be spliced to preserve tensile strength, and the steel strands must be spliced in the same physical location as the optic fibers. Consequently, two delicate operations must be performed in one small area.
Therefore, a need exists for an improved submarine fiber optic cable and a method of installing a fiber optic cable underwater.